The present invention relates to a display panel device, a display panel unit and a display device for use in a liquid crystal display device and the like.
As a display device for a personal computer or other various monitors, a liquid crystal display device has been remarkably widespread. Such a liquid crystal display device is generally constituted in such a manner that a backlight as a planar light source is disposed on a back of a display panel to irradiate a liquid crystal surface of a specified expanse with an even bright light as a whole, and that an image formed on the liquid crystal surface of the display panel can be thereby visualized.
In the case of achieving enlargement of the liquid crystal display device as described above, under the present situation, since enlargement of the display panel itself has limitations, as shown in FIG. 6, a plurality of display panels 2 are arranged, and the display panels 2 and 2 adjacent to each other are adhered together, thus constituting a large-sized liquid crystal display device. In such a case, each of the display panels 2 is referred to as a tile panel.
Heretofore, in the display panel 2, data lines and scan lines for driving liquid crystal have been provided in a matrix fashion, and on two sides of the display panel 2, drive circuit portions 3 and 4 for the data lines and the scan lines are provided, respectively. For this reason, up to now, enlargement of a liquid crystal display device has been previously limited to a formation of four display panels 2 at the maximum, i.e., 2 vertical panels by @2 horizontal panels.
On the contrary, integration of the drive circuit portions 3 and 4 for the data lines and the scan lines in a matrix fashion has been developed as an integrated drive circuit portion, which is provided only on one side of the display panel 2. Thus, a liquid crystal display device extending long in one direction has become formable by connecting many pieces of the display panels 2 in either the vertical or the horizontal direction.
However, when the liquid crystal display device is enlarged as described above, first, there is a problem of a viewing angle characteristic. Specifically, in the case of enlarging the liquid crystal display device, for example, when the viewing angle characteristic of each display panel 2 is set with a center portion of a display area taken as a reference, there occurs such a problem as that it is difficult to see display contents in the periphery of the display area.
For the problem, various proposals have been made in order to improve the viewing angle characteristic on the entire display area of the large-sized liquid crystal display device. Basically, the viewing angle of the display panel 2 depends on a direction of rubbing performed on a substrate constituting the display panel 2, which regulates an aligning direction of the liquid crystal in the display panel 2. For example, in the gazettes of Japanese Patent Laid-Open Nos. Sho 60 (1985)-156048 and Hei 7 (1995)-140461, a liquid display device in which rubbing of a substrate is performed in different directions depending on a position of the display panel 2 in the display area thereof has already been proposed.
As a mode offering a more excellent viewing angle characteristic as compared with a twisted nematic (hereinafter abbreviated as TN) mode typically used in the display panel 2, an in-plane switching (IPS) mode and a vertical alignment (VA) mode are mentioned. Moreover, there is another type of the display panel 2, which is capable of improving the viewing angle characteristic even though a TN mode is used therein. As shown in FIG. 7, the display panel 2 of this type includes: a light collection member 6 for collecting a planar light irradiated from a backlight 5 thereon; and a diffusion member 7 for diffusing the light collected by the light collection member 6 and transmitted through the display panel 2, wherein the collection member 6 is disposed below the display panel 2, and the diffusion member 7 is disposed above the display panel 2. Improvement of the viewing angle characteristic is conceivable by adopting these constitutions into a large-sized liquid crystal display device.
However, in any of the cases as described above, when the liquid crystal display device is enlarged, there is another problem that a size thereof is limited by polarizing plates disposed above and below the display panel 2. As shown in FIGS. 7 and 8, a polarizing plate 8A for controlling light incident onto the display panel 2 is provided above the display panel 2, and a polarizing plate 8B for controlling light emitted from the display panel 2 is provided below the display panel 2. As shown in FIG. 8, for example, in the case of an o (ordinary)-mode, the polarizing plates 8A and 8B have optical absorption axes in directions shown by arrows (a), respectively. These polarizing plates 8A and 8B are severally provided with the direction of the absorption axis thereof based on the rubbing direction of the display panel 2 as a standard. When the liquid crystal display device is of a normally white mode, a state as shown in FIG. 8 is set, where the absorption axis of the polarizing plate 8A is allowed to coincide with a rubbing direction (b) of an upper substrate 2a, and the absorption axis of the polarizing plate 8B is allowed to coincide with a rubbing direction (c) of a lower substrate 2b. When the liquid crystal display device is of a normally black mode, both of the absorption axes of the polarizing plates 8A and 8B are allowed to coincide with the rubbing direction of the upper substrate 2a. 
The directions of the absorption axes of the polarizing plates 8A and 8B, as shown in FIG. 9, depend on an extending direction (d) of a film-like material during fabrication thereof. In order to set the absorption axes of the polarizing plates 8A and 8B in directions approximately diagonal thereto, the polarizing plates 8A and 8B must be laid out aslant on a material 9 when the polarizing plates 8A and 8B are cut out of the material 9 extended in the direction shown by an arrow (d). Such a layout is applicable not only in the case of the o-mode, shown in FIG. 8, but also in the case of e (extraordinary)-mode.
Therefore, each size of the polarizing plates 8A and 8B, which can be cut out, has been forced to be significantly smaller with respect to a width W of the material 9, resulting in limitations of a size of the liquid crystal display device, particularly, a vertical size thereof. Moreover, since the polarizing plates 8A and 8B are laid out aslant to the material 9 and cut out, a yield of the material 9 is lowered, thus hindering the reduction of material costs.
In addition to the above-described problems, in the constitution using the light collection member 6 and the diffusion member 7 as shown in FIG. 7, the enlargement of the light collection member 6 and the diffusion member 7 has limitations, and further, transmission of light through the light collection member 6 and the diffusion member 7 causes an optical loss.
The present invention was made with the foregoing technical problems in mind. A principal object of the present invention is to provide a display panel device, a display panel unit and a display device, which are capable of achieving enlargement thereof and of reducing material costs of the polarizing plates. Another object of the present invention is to provide a display panel device, a display panel unit and a display device, which are capable of improving a viewing angle characteristic even in the case of enlargement thereof.
In order to achieve the foregoing objects, a display panel device of the present invention is characterized in that directions of aligning treatment for two substrates of a display panel are allowed to coincide with a vertical direction and a horizontal direction of the display panel device independently of each other, and directions of optical absorption axes of two polarizing plates are allowed to coincide with the vertical direction and the horizontal direction of the display panel device independently of each other. For example, it is satisfactory that the direction of the aligning treatment for one substrate out of the two substrates is allowed to coincide with the vertical direction of the display panel device, and that the direction of the aligning treatment for the other substrate is allowed to coincide with the horizontal direction thereof. Moreover, optical absorption axes of polarizing plates on both surfaces of the display panel device are allowed to coincide with either the vertical direction or the horizontal direction of the display panel device. In the case when the display panel device is of a normally black mode of a 90 degrees TN type, the both polarizing plates are allowed to coincide with any one of the vertical and horizontal directions of the display panel device, and when the display panel device is of a normally white mode of a 90 degrees TN type, one of the polarizing plates is allowed to coincide with the vertical direction of the display panel device, and the other polarizing plate is allowed to coincide with the horizontal direction thereof.
With such a constitution, the polarizing plates do not have to be obliquely cut out of a material extended in one direction. In this case, larger polarizing plates can be formed out of a material with the equal width, and a waste of the material is reduced. Moreover, when the directions of the optical absorption axes of the polarizing plates are allowed to coincide with a direction of a long axis of the display panel device, a display panel device longer in the long axis direction can be obtained. This is particularly effective in the case where the optical absorption axes of the both polarizing plates are allowed to coincide with the long axis direction of the display panel device, that is, in the display panel device of a normally black mode.
Here, the display panel may be only one, but also a plurality of display panels may be also arranged on one plane. In this case, one polarizing plate is disposed on each of both surfaces of the display panel device so as to cover the whole plurality of display panels. Moreover, when the plurality of display panels are provided, if the directions of aligning treatment for the adjacent display panels are made to differ from each other, viewing angle characteristics can be dispersed on the display panel device as a whole.
Meanwhile, as for combinations of the directions of the aligning treatment for the two substrates constituting the display panel and the optical absorption axes of the polarizing plates disposed on the both surfaces of the display panel, there are eight combinations as below. The display panel device of the present invention can be applied to any of these combinations. Here, when the combinations are represented in an order as: the direction of the optical absorption axis of the polarizing plate on an emitting surface side/the direction of aligning treatment for the substrate on the emitting surface side/direction of aligning treatment for the substrate on an incident surface side/the direction of the optical absorption axis of the polarizing plate on the incident surface side, then the eight combinations are represented as below.
(1) horizontal/vertical/horizontal/horizontal: normally black mode of 90 degrees TN type (o-mode)
(2) vertical/vertical/horizontal/horizontal: normally white mode of 90 degrees TN type (o-mode)
(3) horizontal/horizontal/vertical/horizontal: normally black mode of 90 degrees TN type (e-mode)
(4) vertical/horizontal/vertical/horizontal: normally white mode of 90 degrees TN type (e-mode)
(5) horizontal/horizontal/horizontal/horizontal: normally white mode of parallel alignment type (o-mode)
(6) vertical/horizontal/horizontal/horizontal: normally black mode of parallel alignment type (o-mode)
(7) vertical/vertical/vertical/horizontal: normally white mode of parallel alignment type (e-mode)
(8) horizontal/vertical/vertical/horizontal: normally black mode of parallel alignment type (e-mode).
Among the above combinations, the most preferable in those of the 90 degrees TN type is (1), and the most preferable in those of the parallel alignment type is (5).
When the present invention is conceived as a display panel unit comprising a plurality of modular display panels arranged on one plane, the display panel unit can be characterized in that the plurality of modular display panels are laid out in order that viewing directions showing high contrast of the modular display panels may be directed to a plurality of directions on the whole of the display panel unit, and in order that directions of aligning treatment may be parallel to either a long axis or a short axis of the display panel unit. The display panel unit described above may be provided with the polarizing plates on the both surfaces thereof.
As described above, the viewing directions showing high contrast in each modular display panel are varied, thus viewing angle characteristics on the whole display panel unit can be distributed. In this case, for each set of four pieces of the modular display panels, the viewing directions showing high contrast may be directed to four directions different from one another. Moreover, the modular display panels may be arranged along a direction of the long axis of the display panel unit in order that twisting directions of liquid crystal molecule alignments in the modular display panels may be alternated. In this case as well, the viewing angle characteristics can be distributed.
Furthermore, the present invention can be conceived as a display panel device comprising: a display panel unit; and polarizing plates having optical absorption axes allowed to coincide with directions of either a long axis or a short axis of the display panel unit, characterized in that a plurality of modular display panels constituting the display panel unit are subjected to aligning treatment in the directions of the optical absorption axes of the polarizing plates as standards. Here, as for the modular display panels, those of a so-called IPS mode can be used, which includes: pixel electrodes for applying a drive voltage to the liquid crystal; and common electrodes for generating electric field between the pixel electrodes and the common electrodes in a direction along the surface of the substrate.
A display panel device of the present invention can be characterized in that a plurality of modular display panels arranged on one plane are laid out in such a way that a viewing direction of high contrast in each of the modular display panels may be directed to a direction different from one another for each set of n pieces (n being equal or more than 2) of the modular display panels adjacent to one another. Here, if n equals to 4, the viewing directions of high contrast are set in four directions different from one another for each set of four pieces of the modular display panels. With such a constitution, it is made possible to achieve equalization of the viewing directions of high contrast when the whole of the display panel device is viewed. It is a matter of course that n is not limited to 4, but may be an integer of 2 or more. It is satisfactory that n is properly set in response to a size of the display panel device, desired viewing angle characteristics and the like.
The present invention can be also conceived as a display device, comprising: a display panel including a plurality of modular display panels arranged on one plane and polarizing plates respectively disposed along both surfaces of the modular display panels; a drive circuit for each of the modular display panels; and a light source for irradiating planar light onto the display panel, wherein, in each of the modular display panels, a direction of aligning treatment and directions of optical absorption axes of the polarizing plates thereof are severally coincident with any one of, or both of, the long and short axes of the display panel. In this case, in a pair of the modular display panels adjacent in the directions of the long axis and the short axis of the display panel, it is preferable that a combination of a direction of aligning treatment on one substrate and a direction of aligning treatment on the other substrate in one modular display panel and the combination of the same in the other modular display panel are made different from each other. Thus, the viewing directions of high contrast are made different from each other in a pair of modular display panels adjacent to each other.